1. 1 xDSL

2. 2 Network reference model Core network Access network Transport exchange TP cable fiber WLL Network provider Access provider Service provider Customer Premises Network

3. 3 Evolution of Access Network Evolution based on Twisted Pairs(TP) Evolution based on optical fiber Evolution based on wireless network

4. 4 국내 초고속 가입자 현황 xDSL HFC APT LAN 위성 합계 KT 4,625,841 498,306 5,632 5,129,782 하나로 통신 1,184,629 1,359,675 386,951 2,931,255 두루넷 1,284,963 8,543 1,293,506 온세통신 482,172 6,967 489,139 드림라인 73,075 87,554 3,663 164,192 데이콤 69,630 74,653 144,283 부가통신사업자 4,836 363,632 4,388 372,856 별정통신사업자 49,205 124,854 174,059 합계 5,937,586 3,647,626 1,108,328 5,632 10,699,172 점유율 (%) 55.50 34.09 10.36 0.05 100 2003 년 2 월말 자료 : 한국전산원

5. 5 DSL 기술의 배경 One way to avoid enormous investment for installing optical fiber local loop is to use the traditional copper local loop. The twisted local loop is actually capable of handling bandwidths up to 1.1 MHz, but the filter installed at the end of the line by the telephone company limits the bandwidth to 4KHz. If the filter is removed, however, the entire 1.1 MHz is available for data and voice communications. Thus, DSL technology provides higher data rate in addition to support POTS at the same time.

6. 6 Various xDSL(1) ISDN 2B+D 23B+D HDSL(High data rate Digital Subscriber Line) ADSL(Asymmetric Digital Subscriber Line) SDSL(Symmetric Digital Subscriber Line) VDSL(Very high data rate Digital Subscriber Line) RADSL, MDSL, IDSL, UADSL

7. 7 Various xDSL(2) ADSL2 ADSL2+ VDSL2

8. 8 Characteristics of major xDSL Central Office (PSTN ) Central Office (PSTN ) CO Repeater CO Repeater Line Repeater Line Repeater Line Repeater Line Repeater End User (POTS) Central Office (PSTN ) Central Office (PSTN ) HDSL CO Unit HDSL CO Unit HDSL RT Unit HDSL RT Unit End User (POTS) Headend (Video ) Headend (Video ) ADSL CO Unit ADSL CO Unit ADSL RT Unit ADSL RT Unit End User (Video) PSTN POTS Headend (Video ) Headend (Video ) Optical Network Unit Optical Network Unit VDSL RT Unit VDSL RT Unit End User (Video) POTS VDSL CO Unit VDSL CO Unit PSTN T1/E1 HDSL ADSL/ SDSL VDSL 0.3~1km TP(2 pairs) 1~1.8km0.3~1km TP(2 pairs) TP(1 pair)

9. 9 HDSL T1/E1 rate with 2 TP pairs Internet access, LAN service Mainly used for leased line service for business customers Covers 3.5km(12kf) using 196KHz bandwidth without any repeater Less expensive than the standard T1/E1 leased line service dual duplex: two transceiver 2B1Q Modulation

10. 10 SDSL T1/E1 rate with single pair Data rate; 160kbps-2.048Mbps(symmetrical) Distance: less than 3km 2B1Q

11. 11 ADSL Asymmetric bi-directional digital subscriber line Data rate:1.5- 8 Mbps (downstream), 16-640 kbps (upstream) depending on distance and line quality Distance is up to 5.5km(18kft) DMT(G.992.1, G.992.2) ADSL RT Unit ADSL RT Unit End User PSTN POTS TP 1pair 1.5 ~ 8 Mbps 16 ~ 640kbps Headend ADSL CO Unit

12. 12 Frequency Bandwidth Since data transmission is done on the frequency between 30KHz and 1MHz, ADSL provides data services as well as POTS at the same time. 0.3 3.3 30 138 1104 POTS upstream downstream frequency (KHz)

13. 13 ADSL Modem and DSLAM

14. 14 Line coding Discrete Multitone(DMT) ITU standard(G.992.1, G.992.2) Combines QAM and FDM. The whole bandwidth is divided into 256 channels. For upstream data and control the channel 6 to 30 are used, each using 4KHz. With QAM modulation, available bandwidth is 24x4000x15 = 1.44Mbps. For down stream, channels 31 to 255 are used, and we can achieve up to 224x4000x15=13.4Mbps

15. 15 DMT

16. 16 Bandwidth Division

17. 17 ADSL2 Data rate: 8Mbps(down), 800kb/s(up) Improve ADSL for stability rather than speed. Improved initialization On-line reconfiguration Framing DMT(G.992.3, G.992.4)

18. 18 ADSL2+ Improve the downstream data rate of ADSL. Bandwidth for downstream data transmission: 2MHz downstream data rate 16Mb/s, 1.2km 10Mb/s, 1.8km 7Mb/s, 2.5km Upstream, 1.5Mb/s DMT(G.992.5) However, there is little or no improvement of speed for loops beyond 2.5km.

19. 19 VDSL Very high data rate digital subscriber line Because of distance limitation, fiber cable should be installed up to the curb, and from there twisted pair lines are used up to subscribers. Depending on distances, up to 13-52Mbps(down), 1.5-2.3Mbps(up) Bandwidth: 10MHz VDSL line coding standards ANSI: DMT IEEE: DMT (EFM-Cu for short-reach) ETSI: DMT/QAM ITU-T G.993.1 Because VDSL is used for short distance, there are many technical issued such as crosstalk to be solved.

20. 20 xDSL Comparison Data rate types TPPOTS IDSL128kbps~5.5km1X SDSL768kbps~3.5km up down distance

21. 21 New ADSL 0.5 2 3 4 5 6 7 1 km 거리 50Mb/s 10Mb/s 6Mb/s 1Mb/s VDSL ADSL2+ ADSL ADSL2+ VDSL2

22. 22 VDSL2 Adopts ADSL ‘ s new features Backward compatibility to ADSL family Possible new features Frequency beyond 12MHz 100Mb/s at 1km Etc.

23. 23 Migration Strategy Copper Loop DLC FTTC FTTH Wire Plant Neighborhood Curb Premises DSLAM up to 8Mbps up to 52Mbps 155Mbps and beyond DLC ONU

24. DSL Terminology xDSL = Physical layer technologies allowing transport of digital information over the copper loop. xDSL=x Digital Subscriber Line ADSL=Asymmetric Digital Subscriber Line RADSL=Rate-Adaptive Digital Subscriber Line UAWG=Universal ADSL Working Group (universal ADSL, ADSL Lite, G.Lite, splitterless ADSL) SDSL=Symmetric Digital Subscriber Line HDSL=High Bit-Rate Digital Subscriber Line HDSL2=High Bit-Rate Digital Subscriber Line, 2nd generation SHDSL=Single-pair High Bit-Rate Digital Subscriber Line IDSL=ISDN Digital Subscriber Line VDSL=Very High-Speed Digital Subscriber Line DSLAM=Digital Subscriber Line Access Multiplexer

25. 25 HFC(Hybrid fiber-coaxial)

26. 26 HFC Overview HFC networks use a hybrid of fiber optic and coaxial cable to make the cable network bidirectional (two-way). The use of fiber-optic cable reduces the need for amplifiers down to 8 or less. Coaxial network has a tree & branch structure. An area served by a SO is divided into several cells. The size of a cell is decided by the number of subscribers. Head end ONU splitter Cable modem PC Set top box TV

27. 27 HFC 망 Distribution center (SO) PP ISP Outdoor optical RTX (ONU) TBA splitter Tap-off Cell 1 Cell N Coaxial cable CMTS CM broadcast H/E CM: cable modem CMTS: cable model termination system TBA: trunk bridge amplifier Optical RTX Power supply PP: program provider SO: system operator

28. 28 Components ONU(Optical Network Unit) Transforms between optical signals and RF signals in a cell. TBA Guarantee the loss of line signal of coaxial cables. Splitter Split one RF signal into more than two RF signals. Tap-off It distributes equally RF signal into subscriber terminals.

29. 29 Frequency bandwidth The downstream data occupies 450-552MHz band. This band is divided into 6MHz. The upstream data occupies 5-42MHz band, which is also divided into 6MHz channels. The 5-42MHz frequency band for upstream is very susceptible to noises by consumer electronics devices and signals caused by HAM, CB radios. For this reason, The low bit rate modulation technique such as QPSK is used for stability. upstream Analog broadcast Internet Digital broadcast Value added services 5 42 54 450552 750 MHz

30. 30 Data rates Data rates depending on modulation techniques of DOCSIS modems upstream Downstream bandwidth 1.5MHz 6MHz modulation Data rate QPSK 16QAM 64QAM 256QAM 2.5Mbps 5Mbps 27Mbps 40Mbps

31. 31 Characteristics One cell serves up to 500-2500 subscribers. Bidirectional transmission Limitation of data rate When 100 subscribers use at the same time, data rate is reduced to less than 300kbps(downstream). Because of tree & branch structure, the transmission quality is deteriorated by signal interruption.

32. 32 국내 HFC 망 연혁 1995 년 종합유선방송 ( 케이블 TV) 사업 개시 PP(Program provider): 프로그램 공급자 SO(System operator): 지역 방송국 광역시, 대도시 1 차 53 개 지역 지역 중소 도시 2 차 24 개 지역 중계유선 3 차 NO(Network operator): 케이블 TV 분배망 (PP-SO): 파워콤, KT( 위성 ) 케이블 TV 전송망 (SO- 가입자 ): 파워콤, SO 의 HFC 망 케이블 모뎀을 통한 인터넷 사업 시작 1997 년 KEPCO 양방향 시버 서비스 성공 1998 년말 두루넷 (KEPCO 의 HFC 망 사용 ) 사업 시작 1999 년 하나로, 2000 년 온세 통신 등 다수 사업자 참여 HFC 망 : KEPCO 1 차 지역, 데이터 HFC 망 구축 2000-2002 년 초고속 가입자 사업 활성화 KT 시설분 SO 매각, 중계유선의 SO 전환 파워콤 분리 인터넷 가입자 증가로 데이터 HFC 망 시설 폭증 ( 하나로, 두루넷, SO 등 HFC 자가망 구축 ) 2003 년 디지털 케이블 TV 도입 개시 자료 : 파워콤㈜ KRNET2004 발표자료

33. 33 국내 인터넷 가입자 현황 전체 가입자 증가와 마찬가지로 현재 완만한 증가 추세로 인터넷 가입자의 포화 상태에 이르렀음을 알 수 있다. 전체가입자 HFC 망가입자 2000.12 2001.2 2002.12 2003.122004.4 자료 : 파워콤㈜ KRNET2004 발표자료 398 만 139 만 780 만 262 만 1,040 만 1,118 만 1,143 만 355 만 383 만 402 만

34. 34 Standards CableLabs, DAVIC, IEEE 802.14, ATM Forum, IETF 의 IP over Cable Data Network CableLabs(Cable Television Laboratories Inc.) Non profit organization composed of cable modem manufacturers. CableLabs standards are adapted by ANSI, ITU-T Also performs certificates. DOCSIS(Data Over Cable Service Interface Spec.) DOCSIS 1.0(1999): DOCSIS 1.1: DOCSIS 2.0(2001): Digital settop box standards: Opencable Cable Network Interface Standard(SCTE40/DVS313)

35. 35 DOCSIS cable modem DOCSIS 1.0(1999 년 ) First commercialized standards Bidirectional data transmission DOCSIS 1.1(2001 년 ) Improve OoS functions DOCSIS 1.0 can be upgraded to DOCSIS by software. DOCSIS 2.0(2002 년 ) Improve upstream data rate: 30Mbps Symmetrical bidirectional service H/W upgrade

36. 36 HFC MAC Credit-based MAC For upstream transmission, the headend grants the right to send data to cable modems. CRA(Collision Resolution Algorithm) When cable modems send credit requests collision may happen, When it happens, the headend detects the collision, and notifies cable modems of it. Then the cable modems backoff and retry after random intervals.

37. 37 Future Speed improvement Frequency bandwidth can be expanded upto 1.5Gbps, the speed can be increased upto 100Mb/s. Downsizing of cells The current distance from ONU to subscribers which is about 1km will be decreased to less than 500m. Improve network monitoring system.

38. 38 SDH (SONET)

39. 39 Multiplexing of Telephone Lines

40. 40 Multiplexing of Digital Signals

41. 41 Table 6.1 DS and T lines rates ServiceLine Rate (Mbps) Voice Channels DS-1T-11.54424 DS-2 DS-2T-2 6.312 6.31296 DS-3 DS-3T-3 44.736 44.736 672 672 DS-4T-4274.1764032 Digital Hierarchy

42. 42 Table 6.2 E line rates E Line Rate (Mbps) Voice Channels E-1 2.048 2.048 30 30 E-2 8.448 8.448 120 120 E-3 34.368 34.368 480 480 E-4139.2641920 Digital Hierarchy (Europe)

43. 43 Synchronous Digital Hierarchy(SDH) PDH DS-0 0.064 1 DS-1 T-1 1.544 24 DS-2 T-2 6.312 96 DS-3 T-3 44.736 672 DS-4 T-4 274.176 4032 SDH STM-1 OC-3 155.52 STM-4 OC-12 622.08 STM-16 OC-48 2488.32 STM-48 OC-192 9953.28

44. 44 Synchronous Digital Hierarchy(SONET) STSOCRate (Mbps)SPE (Mbps)User (Mbps) STS-1OC-151.8450.1249.536 STS-3OC-3155.52150.336148.608 STS-9OC-9466.56451.008445.824 STS-12OC-12622.08601.344594.432 STS-18OC-18933.12902.016891.648 STS-24OC-241244.161202.6881188.864 STS-36OC-361866.231804.0321783.296 STS-48OC-482488.322405.3762377.728 STS-192OC-1929953.289621.6049510.912

45. 45 SONET transport network

46. 46 2.5Gbps (POS) GSRGES 동선 FLC STM-4 (2.5G) Edge Router (7500) ADM DSC (D/MUX) FLC DSC (D/MUX) ADM CSU OC3 OC3/ OC12 Internet MTU STU ADSL (1.5M~8Mbps) DSLAM B-RAS DS3/ OC3 DS3/ OC3 CO( 수용국 ) POP( 주노드국 ) 수용국 ADM LAN C LAN A LAN B SONET/SDH T1 CSU LAN D T1 1.544 Mbps T1 (1.544Mbps) 64Kbps 28 STS-1 (45M) STS-N … OC-N … 24 1 1 1.544Mbps … STS-1 64Kbps 28 STS-1 STS-N … … 24 1 1 1.544Mbps … STS-1 TDM multiplexing/Circuit switching No Statistical multiplexing T1 1.544 Mbps Home TDM-based transport network

47. 47 SONET frame